Thermionic valve



Aug. 15, 1933. w R BULUMORE 1,922,926

THERMIONIC VALVE Filed Oct. 26, 1952 INVENTOR William R. Bullimore ATTORNEY Patented Aug. 15, 1933 UNlTED STATES PATENT OFFICE Application October 26, 1932, Serial No. 639,695, and in Great Britain August 21, 1931 5 Claims. (01. 250 2'z.5)

This invention relates to thermionic valves and more particularly to amplifying valves of the kind comprising an electron emitting cathode, an anode and a grid electrode interposed between anode and cathode and intended to control the discharge between the anode and cathode.

The object of the invention is to improve the performance of a thermionic amplifying valve of this type.

It is well known that the characteristics of a thermionic amplifying valve can be greatly modi-- between the control grid and the main anode for the purpose of increasing the mutual conductance of the valve as compared with the mutual conductance which would be obtainable from a three electrode valve having a similar cathode and control electrode, an auxiliary anode being connected to the main anode in such a way that the space current collected by the auxiliary anode passes through a suitable impedance to the out-- put apparatus and the auxiliary anodeis held at a positive potential lower than that of the main anode.

The invention will now be more particularly described with reference to the accompanying drawing which illustrates the electrode system of a thermionic valve constructed according to the preferred embodiment of the invention and in which:

Figure 1 is a diagrammatic partly sectional elevation, and

Figure 2 a diagrammatic sectional plan.

As shown in the drawing the electrode system comprises a flattened tubular cathode 1 heated by an internal filament 2, a control grid 3, an anode 4 surrounding the grid and an auxiliary anode 5 interposed between the anode 4 and the grid 3.

The control grid 3 consists of a wire 3a wound upon a pair of parallel conductor supports 3b so as to form a flattened grid structure closely surrounding the cathode. The auxiliary anode 5 consists of a wire 5a Wound on a pair of parallel conductor supports 5b so as to form a rectangular foraminous grid structure concentrically sur-- rounding the grid 3.

The main anode may comprise a pair of sheets or plates 4a welded or otherwise secured to a pair of conductor supports 6 secured in the pinch 7, each plate 4a being bent to a trough-like shape so that the two plates form a tubular anode of rectangular section, and one or both of the plates ea may be cut away to form windows covered with wire mesh 8 as shown, for the purpose of increasing therate of loss of heat by radiation from the cathode and thereby preventing overheating of the anode. p, a

The conductor supports upon which the grid and auxiliary anode wires are wound and also the cathode 1 may be conveniently located by sheets of mica or other suitable insulating material 9 attached to the anode 4 and designed to hold the electrodes firmly in their proper relative positions.

The auxiliary anode 5 is connected to the anode 4 within the valve by means of a resistance 10 consisting of a coil of wire connected at one end to a conductor 11 welded to one of the conductor supports 51) and a conductor 12 welded to one of the anode conductor supports to which the external anode terminal of the valve is connected.

Theresistance 10 carries the whole of the space current collected by the auxiliary anode so that owing to the potential drop through this resistance'the auxiliary anode is held at a positive potential lower than the potential of the main anode.

The value of the resistance 10 may be varied within wide limits. In the case of a valve designed to be used with a working anode potential of 200 volts and an anode current of 45 milliamperes and in'which the space current is approximately equally divided between the main anode and the auxiliary anode, it is found that good results are obtained with a resistance of about 20 ohms corresponding to a potential difference of about 0.5 volts between the main anode and the auxiliary anode. Greater values of resistance corresponding to greater potential differences between the main anode and the auxiliary anode may however be employed.

It is found in practice that the arrangement of the foraminous auxiliary anode and the main anode in accordance with the present invention increases the voltage amplification factor of the valve as compared with that of an ordinary three-electrode valve of the same impedance having an exactly similar cathode and grid electrode. In other words, the valve constructed as herein l .iliary anode is held at a positive potential lower than that of the main anode, said impedance described will have a higher mutual conductance than that of the three-electrode valve, although the total emission provided by the cathode and the form and arrangement of the control electrode is the same in each case.

It is believed that the explanation of this effeet is to be found in the fact that secondary elec trons are produced by the impact of electrons upon the anode. In the case of the ordinary three electrode valve these secondary electrons increase the space charge, thereby decreasing the mutual conductance of the valve. a valve constructed in accordance with the present invention however, a substantial part of the electron stream passes through the auxiliary foraminous anode to the main anode or plate electrode and the secondary electrons produced space current due to=the reduction in effective space charge is utilized and an increase in the slope of the characteristic curve or mutual conduct'ance results.

It will be understood that although the invention is-not limited'in its application: to any particular class of thermionic amplifying valve it ise'specially intended-to be applied to valves such as are used in wireless receiving apparatus and which are capable of dissipating considerably more energythan they absorb under ordinary working conditions; 7

I claim:

1. A thermionic amplifying valve comprising an electron emitting cathode, an anode, a grid electrode interposed between the anode ,andcathode for controlling the electrical discharge betweenth'e'cathode andanode, aforaminous auxiliary anode mounted between the main anode and the control grid, and a connection between said auxiliary anode and said" main anode comprising an impedance forming apart of the amplify-lng valve and which forms the sole outlet path for the space current passing fronrthe cathode to the said-auxiliary anode, whereby theauxhaving a value to'cause-substantially equal space currents to flow to the two said anodes.

2. A thermionic amplifying valve; comprising .an electron emitting cathode, a main anode, a grid electrode interposed between the anode and cathode for controlling the electrical discharge In the case of between the cathode and anode, and a formaminous auxiliaryanode mounted between the main anode and the control grid, a resistance connected between said main anode and said auxiliary anode, said resistance forming a part of the valve and constituting the sole path whereby the space current collected by the auxiliary anode passes to the anode, for. maintaining the auxiliary anode at a positive potential lower than that of. the main anode, said resistance having a value to cause substantially equal space currents to How tothe two said anodes.

3. A four-electrode thermionic amplifying Valve comprising a cathode, a main anode and a control grid interposed between the said anode and'cathode and a foraminous auxiliary anode disposed between the main anode and the control grid and means forming part of the valve and connecting said auxiliary anode to the main anode wherebythe space current, collected by the auxiliary anode, passes out solely through the main anode and the auxiliary anode-is held at a positive potential lower than thatof the main anode due to the potential drop in said connecting means, said means being of such value that the space current collected by the auxiliary anode is substantially one-half of the total space current;

4. A thermionic amplifying valve, comprising a cathode, amain anode, and a control grid interposed between the said anode and cathode, a foraminous auxiliary anode, mounted between the main anode and the control grid, a resistance forming part of the valve, said auxiliary anode being connected to saidmain anode solely through said resistance, whereby the space current 001- lected'by the auxiliary anode'passes out from the valve solely through the main anode and the working potentialof the auxiliary anode is thereby maintained lower than the working potential of the main anode, for maintaining a potential diiferencebetween these anodes of not materially less than 015' volts, the value of said resistance being such" that the space current collected by the auxiliary anode is substantially the same as that passing directly to the main anode.

5. A thermionic amplifying valve comprising a thermionic cathode electrode; a control electrode for said cathode electrode; means for substantially equally dividing the current which passes beyond said control electrode, said means comprising an anode electrode and a foraminous 

